The present invention relates to force sensors, and in particular, to an electromechanical force sensor measuring both force magnitude and angle.
Force sensors, such as strain gauges attached to an elastic carrier, are well known in the art for producing an electrical signal proportional to force. Generally, strain gauges provide a change of resistance as the conductive material of the strain gauge is stretched or compressed. Strain gauges are designed to be sensitive principally along a single axis and will be termed “single axis sensors” producing a magnitude and sign of force in one dimension.
The measurement of force magnitude and direction in two or more dimensions (angle) may be accomplished by placing a number of single axis sensors along different orthogonal axes. Each sensor provides a vector component of the force which may be summed to produce a single vector in multiple dimensions.
Measurement of force magnitude and angle may be desirable in certain therapeutic and/or exercise equipment where knowledge of not only how hard a user is pushing, for example, on the pedal of a stationary bike, but also the angle in which the user is pushing can be important in providing the user with feedback for therapy or training or in providing sophisticated control of the training device.
Extraction of force angle from multiple, single-axis sensors is difficult, requiring accurate alignment and calibration of multiple sensors. Further, cross talk between sensors, caused by their sensitivity to off-axis forces, introduces error in force angle when derived by this method.